1. Field of the Invention
The present invention relates to electrical connectors and more specifically, the present invention relates to connectors having a unique arrangement of contacts or terminals having a fusible member attached thereto, that allows for much higher coplanarity while simplifying the connector manufacturing and assembly procedures.
2. Description of the Related Art
Electrical connectors are used to place electrical devices, such as printed circuit boards, in communication with one another. An electrical connector may be thought of as having two portions, one portion of which connects to a first electrical device and the second portion of which connects to a second electrical device to be put into communication with the first device. To connect the two devices, the two portions of the electrical connector are mated together.
Each portion of the connector includes one set of contacts or terminals adapted to communicatively couple to an electronic device and a second set of contacts or terminals adapted to matingly couple to the other connector portion. This can be readily accomplished by designating one portion of the connector as having “male” contacts or terminals adapted to couple to the other connector portion's “female” contacts or terminals. Regardless of the specifics of the design of the contacts or terminals, the two connector portions should be adapted to be easily connected and disconnected from each other to respectively electrically link and unlink the electrical devices to which they are connected.
Accordingly, each connector portion is fixedly connected to an electronic device through its remaining set of contacts or terminals. The contacts or terminals may be removably or permanently connectable to the electrical device; however, it is usually desired that the connector portion be secured to the electrical device through some physical mechanism. Typically, the connector portions are secured to electrical devices by fusing the contacts or terminals to contact pads or the like formed on the electrical device.
Recently, there has been a trend toward miniaturization of most electrical devices. As electrical devices become smaller and more complex, the electrical connectors used with these devices must also become smaller and must be able to accommodate the more complex devices. One problem with miniaturized electrical connectors arises from the increased precision of placement necessary to produce the proper positioning and connection of the connector contacts or terminals onto the device. This problem is exacerbated by the ever increasing input/output (I/O) density requirements demanded of the progressively smaller electrical connectors by increasingly miniaturized electrical devices. With increased pin counts (e.g., greater number of terminals) in each connector, it becomes more and more difficult to maintain desired levels of co-planarity while maintaining contact of all of the terminals to a substrate or PCB.
One means of addressing the need for increased I/O density is to provide an arrayed connector. Such a connector can provide a high-density two-dimensional array of contacts or terminals for interfacing with an electrical device. However, arrayed connectors present attachment difficulties regarding connection to devices (i.e., circuit boards or substrates) since most of the contacts or terminals must necessarily be positioned in the interior of the two-dimensional array area and are accordingly difficult to align upon connection, visually inspect, and/or repair.
One attempt to provide a high-density electrical connector interface has been to use a ball grid array (BGA). The BGA offers the advantages of a precisely formed high-density array of contacts or terminals available to interconnect with a substrate. The use of a BGA is thought to overcome conventional problems with co-planarity (e.g., to maintain co-planarity at about 0.004″, for example) and to ensure that all contacts or terminals are securely soldered to pads on a PCB when the connector is mounted and reflowed to the PCB.
However, the use of a BGA has many disadvantages. First of all, the use of solder balls greatly complicates the connector manufacturing process because an additional reflow step is required and the use of special equipment is also required. In addition, either the connector body and/or contacts or terminals must be modified to include recesses or solder ball holding structures, or special assembly equipment must be used to hold the solder balls in place until the solder balls can be reflowed to be connected to the tails of conductive contacts or terminals provided in the housing of the connector. After the solder balls have been reflowed a first time so as to be attached to the tails of the contacts or terminals, the entire connector must be reflowed again so that the solder balls can make the necessary electrical and mechanical attachments to conductive pads on a PCB upon which the connector is being mounted. A further problem may occur when the solder balls are attached to gold-plated tail portions of the contacts or terminals, during which process the gold of the tail portions of the contacts or terminals can mix with the tin/lead of the reflowed solder ball which can cause problems with gold embrittlement.
In addition to the above-described problems, variations in the dimensions and/or placement of solder balls at the interface can lead to an uneven or non-coplanar interface and intermittent or poor electrical contact. Also, the presence of oversized or extra solder balls present in the connector interface, or the uncontrolled spreading of the solder balls during the multiple reflow steps can result in shorted connections and degraded connector performance. In addition, the tails of the contacts or terminals are inserted and attached at different depths within the various solder balls so as to create problems with co-planarity. Furthermore, the solder joints created by the solder balls between the contacts or terminals and the pads on the PCB is not as reliable and may not withstand twisting or distortion of the connector body which may occur. That is, the solder joints created using solder balls are not as flexible and may not withstand the stresses applied to the joints when the connector body bows, twists or is distorted in shape.
One alternative to the use of a BGA is described in U.S. Pat. No. 6,679,709, in which circular columns of solder 6 are used instead of solder balls. The circular columns of solder 6 have an elongated cylindrical bar-shaped configuration and in fact are formed by cutting pieces of solder wire. These circular columns of solder 6 are inserted between a pair of bar-like pieces 12 which are then bent to allow claws 13 to grip and hold the solder 6 on the respective terminal or pin 5 such that a longitudinal axis of the circular column of solder 6 is perpendicular to a mounting plane of a PCB or circuit board to which the solder 6 and connector is to be attached. Thus, the solder holding assembly (elements 12, 13, 14) must be arranged perpendicular to the main body 10 of the contact or terminal 5, which complicates the manufacturing and assembly of the contacts or terminals 5 in the connector body. In addition, because the circular columns of solder 6 may have different lengths and may be mounted at different positions with the solder holding assembly (12, 13, 14) of each terminal, many problems with co-planarity may result. Thus, this complicated tail assembly of the contacts or terminals 5 makes manufacturing and assembly more difficult and may cause rather than solve co-planarity problems.
Another alternative is the use of solder-bearing contacts in which the solder has been crimped to the contacts, as shown in U.S. Pat. No. 4,597,628, for example. In this patent, a solder bearing edge clip 10 has arms 15, 16 with arcuate fingers 18, 19 having solder wires 30 attached thereto. The attaching process involves inserting solder wires 30 into openings at the ends of the fingers 18, 19, closing or crimping the fingers to close the openings so as to indent the solder wires 30 as shown in FIGS. 3 and 12. The solder is then melted to attach the arms 15, 16 or 75, 76 to the pads 12 of the substrate 11 as seen in FIGS. 4 and 13. In most of the embodiments shown in this patent, the solder wire is spaced from the outer surfaces of the fingers 18, 19 or 68, 69 because the fingers 18, 19 or 68, 69 must be able to reliably hold the substrate. FIGS. 11A and 11B show an embodiment where the solder wire 71′ projects very slightly from the finger ends so that when the substrate is inserted, the solder wipes across the contact pad 12 to improve the resulting solder joint. However, with this structure, there is no way to control how far the solder projects from the finger ends and thus, no way to ensure that the substrate is reliably held in the arms. If the finger ends are crimped too much, excessive solder will project from the finger ends and it may not be possible to reliably hold the substrate between the fingers. If the finger ends are not crimped enough, the solder will not project from the finger ends. In addition, if fingers 18, 19 or 68, 69 are bent, twisted or having varying dimensions due to manufacturing tolerances, there may be an air gap between the pads 12 and the fingers 18, 19 or 68, 69 and solder. This air gap may not be filled by the solder during reflow because the solder may not be sufficiently wicked or moved toward the pad during reflow. Thus, there may still be problems with reliably forming or soldering electrical connections between fingers 18, 19 or 68, 69 and the pads 12.
In fact, this is one of the most significant problems with electrical connectors in which conductive contacts or terminals are to be joined to conductive elements on a substrate. Because of twisting or flexing of the connector or variations in size, shape, or arrangement of the contacts or terminals in a connector body, an air gap may exist between the contact or terminal and a conductive pad to which it is to be attached before the reflow process is performed. The current designs and arrangements of contacts or terminals in the connectors do not provide for a consistently reliable solution for eliminating the air gap during reflow, and do not ensure that each contact or terminal is securely connected to the conductive pad on a substrate to which the connector is mounted.